The present invention relates to hydrogel compositions for direct-write printing applications, and more specifically, to shear-thinning, thermo-responsive compositions for 3-dimensional (3D) printing that are capable of crosslinking in a liquid and/or hydrogel state.
Patterned hydrogels are of interest for a broad set of applications including drug delivery and tissue engineering. One emerging technology for patterning hydrogels is 3D printing, a form of additive manufacturing in which a 3-dimensional object is constructed one layer at a time. The engineering of 3D printers has matured since the 1980s when 3D printing was first developed for industrial-scale rapid prototyping. Temperature- and pH-responsive hydrogels have been demonstrated to have application in drug delivery and biomedicine. One of these is PLURONIC F127, a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer, attractive because of its thermo-reversible gel-forming properties in aqueous solution. A drawback of the F127 gel is its low yield strength. A high yield strength is desirable for tissue engineering and implantation applications. Another drawback of the F127 gel is its inability to form covalent crosslinks as an aqueous liquid and as a hydrogel. The F127 gel is believed to comprise entangled micelles of self-assembled PEO-PPO-PEO triblock copolymer, which are bound by non-covalent interactions. The micelles easily move past each other under shear, thus the low yield strength.
As 3D printing becomes more central to emerging biomedical technologies, a need grows for aqueous 3D printable inks that are crosslinkable as hydrogels while possessing thermal, rheological, and mechanical properties suitable for 3D printers. Preferably, these inks are “drop-in” materials conforming to the current requirements for 3D printer inks.